(a) Field of the Invention
The present invention relates to a diesel engine, and more particularly, a method and apparatus for controlling a diesel engine equipped with a turbocharger.
(b) Description of the Related Art
A diesel engine may be provided with a turbocharger in order to increase an output power of the engine, to reduce the emission, or to enhance fuel consumption.
When the turbocharger is overheated, oil used for lubrication and cooling of the turbocharger may catch a fire.
The diesel engine shows merits on fuel consumption and output torque, but it shows drawbacks in exhaust gas. That is, although the diesel engine produces less carbon monoxide CO and hydrocarbon HC, it produces more nitrogen oxide (typically, called NOx) and particulate matters because of its high temperature of the combustion chamber caused by its high compression ratio.
Typically, particulate matters can be reduced by combustion control. However, an emission control scheme for reducing NOx may result in an increase of particulate matters, and an emission control scheme for reducing particulate matters may result in an increase of NOx. Therefore, it is very difficult to reduce both the NOx and particulate matters at the same time.
Usually, a diesel engine is provided with a diesel catalyzed particulate filter (CPF) for reducing the particulate matters.
The CPF collects the particulate matters exhausted by the engine, and when more than a predetermined amount of the particulate matters are collected, the CPF is regenerated by burning the particulate matters collected in the CPF in increasing the exhaust gas by employing a post-injection.
On the other hand, a diesel engine is typically provided with an exhaust gas temperature sensor that senses an exhaust gas temperature at an upstream side of a turbocharger. Such a detection of the exhaust gas temperature is useful for preventing an overheating of the turbocharger, for limiting the exhaust gas temperature, and for preventing an overheating of the CPF.
In addition, a lambda sensor is typically provided at a downstream side of the turbocharger in order to measure an air/fuel ratio for the purpose of controlling EGR and adjusting fuel injection.
Thus, an engine control unit (ECU) controls the fuel injection and post-injection, based on the data obtained by the exhaust gas temperature sensor and the lambda sensor located at the upstream and downstream sides of the turbocharger respectively.
However, the exhaust gas temperature sensor located at the upstream side of the turbocharger may have a very short lift time and may be easily become malfunctioned because it is always exposed to very hot exhaust gas and it may easily gather particulate matters. In the case of malfunctioning of the exhaust gas temperature sensor, the exhaust gas temperature may not be controlled such that the turbocharger may be overheated to catch a fire, and the regeneration of the CPF may not be appropriately controlled.
Furthermore, such an employment of the exhaust gas temperature sensor at the upstream side of the turbocharger increases the total work process and thus decreases productivity for manufacturing a vehicle.
Recently, some researches are made in order not to employ the exhaust gas temperature sensor but instead, to employ a method to estimate the exhaust gas temperature.
As an example, Japanese Patent Laid-Open Publication No. 2005-351106 discloses that the exhaust gas temperature can be measured by a heater resistance of an air/fuel ratio sensor.
In addition, Japanese Patent Laid-Open Publication No. 2006-161625 discloses that the exhaust gas temperature can be estimated based on an impedance of the lambda sensor and the heating amount of the heater installed therein.
In addition, Japanese Patent Laid-Open Publication No. 1997-049448 discloses that the exhaust gas temperature can be estimated based on an intake air amount and a target air/fuel ratio.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.